Field of the Disclosure
This disclosure is directed to a method of reducing vanadium pentoxide to vanadium(III) oxide employing solid inorganic reducing agents. This disclosure is also directed to an electrode comprising the vanadium(III) oxide and an electrochemical cell or battery comprising the electrode.
Discussion of the Background
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Transition metal oxides have been studied and applied in areas that span photocatalysis, magnetism, conductivity and superconductivity, and ferroelectricity (Wang et al. Nature Materials, 2003, 2, 402; Law et al, Nature Materials, 2005, 4, 455; Rodriguez et al. Science, 2007, 318, 1757—each incorporated herein by reference in its entirety). Vanadium oxides, VOx, in which the vanadium ion exists in a range of oxidation states from +2 to +5, have been the focus recently because of their potential in optical switching devices, sensors, catalysts, electrochemical devices and high-energy lithium batteries (Wang et al. Chemistry of Materials, 2006, 18, 2787; Kondratenko et al. Applied Catalysis A, 2007, 319, 98—each incorporated herein by reference in its entirety). For instance, vanadium pentoxide (V2O5) offers a theoretical capacity of 442 mAh g−1, which is higher than those of the commercial cathode materials presently used (Cao et al, Angewandte Chemie, 2005, 117, 4465—incorporated herein by reference in its entirety). Vanadium(III) oxide (V2O3) also offers a high specific capacity (1070 mAh g1) but there are limited studies on vanadium(III) oxide because it is challenging to obtain pure vanadium(III) oxide (Li et al. Journal of the Electrochemical Society, 2004, 151, A1878—incorporated herein by reference in its entirety). When vanadium pentoxide is reduced to vanadium(III) oxide, many unwanted lower valent vanadium oxides are formed. Vanadyl sulfate (VOSO4) solution, an electrolyte for vanadium flow batteries, is formed by treating vanadium pentoxide with sulfuric acid. The disadvantages of this method are: the process is hazardous because the reaction is endothermic and requires heating a corrosive acidic solution, and the vanadyl sulfate solution often contains suspended impurities, such as other vanadium oxides, which are hard to remove.
Hausen et al. (U.S. Pat. No. 3,410,652) disclosed a process for producing vanadium(III) oxide from ammonium metavanadate. More specifically, the reference relates to a continuous process for thermally reducing ammonium metavanadate in an atmosphere of hydrogen in a temperature ranging from 580-950° C.
Dormehl et al. (U.S. Pat. No. 7,073,774) disclosed a process for producing a vanadyl sulfate solution. A suspension of vanadium(III) oxide is formed in sulfuric acid and a strong oxidizing agent is added to the vanadium(III) oxide suspension to produce the vanadyl sulfate solution.
Kazacos et al. (U.S. Pat. No. 7,078,123) disclosed a high energy density (HED) electrolyte solution for use in an all-vanadium redox cell. The solution contains a 50:50 ratio of trivalent and tetravalent vanadium ions and stabilizing compounds such as inorganic phosphates and ammonium compounds.
In view of the foregoing, the objective of the present disclosure is provide a method for producing pure crystalline vanadium(III) oxide for applications such as storage materials, resistive materials, magnetic and optical switches and gas sensors.